A geomagnetic paleointensity stack between 0.8 and 3.0 Ma from equatorial Pacific sediment cores
A geomagnetic paleointensity stack between 0.8 and 3.0 Ma from equatorial Pacific sediment cores
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DOI：
10.1029/2005gc001001
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发表时间：
2005-11
期刊：
影响因子：
3.7
通讯作者：
T. Yamazaki;H. Oda
中科院分区：
文献类型：
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作者：
T. Yamazaki;H. Oda
我们已经进行了古地磁研究的6个沉积物芯取自赤道太平洋，三个从西加罗林盆地和三个从Manihiki高原，在松山和晚高斯年代的相对paleointensity叠加。岩芯底部年龄为1.2 ~ 3.0Ma。沉积物的磁性颗粒大小和矿物学的代理显示小downcore变化，因此适合于估计相对古强度。通过将磁浓度（磁化率和/或无滞后剩磁（ARM））的变化与目标氧同位素（δ 18 O）曲线相关联来控制岩心的年龄。Manihiki高原的所有岩心显示，随着沉积速率的降低，经ARM和等温剩磁（NRM）归一化的天然剩磁（NRM）强度向上降低。这种趋势在转换为相对古强度之前被去除。这一观察结果意味着沉积速率的变化会影响相对古强度的估计。在不确定的年龄范围内，六个岩心的相对古强度记录相互吻合。我们在调整年龄后构建了0.8 - 3.0 Ma之间的叠加曲线（赤道太平洋古强度叠加EPAPIS-3 Ma）;整个记录中叠加的岩心数量为3 - 4个。准周期性的古强度低值出现在EPAPIS-3 Ma，相应的古强度低值可以在以前发表的记录中找到，并有一些年龄上的变化。至少，部分古强度极小值似乎伴随着地磁漂移。在Matuyama-Gauss边界和此后的记录中没有观察到古强度变化的“非对称模式”。谱分析表明，在松山年代和高斯年代晚期的古强度变化中可能存在着10万年前的轨道偏心率频率。
We have conducted a paleomagnetic study of six sediment cores taken from the equatorial Pacific, three from the West Caroline Basin and three from the Manihiki Plateau, in order to make a relative paleointensity stack during the Matuyama and late Gauss Chrons. The age of the bottom of the cores ranges from 1.2 to 3.0 Ma. The sediments show little downcore changes in the proxies of magnetic grain size and mineralogy and are hence suitable for estimating relative paleointensity. The age of the cores is controlled by correlating variations in magnetic concentration (magnetic susceptibility and/or anhysteretic remanent magnetization (ARM)) to target oxygen‐isotope (δ18O) curves. All cores from the Manihiki Plateau show an upward decrease of the natural remanent magnetization (NRM) intensity normalized by ARM and isothermal remanent magnetization (IRM) with a decrease in sedimentation rate. Such a trend was removed before being converted to relative paleointensity. This observation implies that a sedimentation‐rate change can affect relative paleointensity estimation. Relative paleointensity records from the six cores coincide well with each other within uncertainty of age. We constructed a stacked curve between 0.8 and 3.0 Ma (the equatorial Pacific paleointensity stack EPAPIS‐3Ma) after adjusting age; the number of cores stacked is three to four throughout the record. Quasiperiodic paleointensity lows occur in the EPAPIS‐3Ma, and corresponding paleointensity lows can be found in previously published records with some shifts in age. At least, parts of the paleointensity minima seem to be accompanied by geomagnetic excursions. The “asymmetric sawtooth pattern” of paleointensity variations is not observed at the Matuyama‐Gauss boundary and thereafter in our record. A spectral analysis shows that ∼100 kyr orbital eccentricity frequency may exist in paleointensity variations during the Matuyama and late Gauss Chrons.